An example of image forming apparatuses, such as a laser printer, includes a detachable process cartridge in the main body.
Such a process cartridge is generally provided with a photosensitive drum, a charging device, and a developing unit. The photosensitive drum is rotated at a constant rotational speed during image formation. The surface of the photosensitive drum is uniformly charged by the charging device with this rotation. When the uniformly charged portion is selectively exposed to light, a static latent image is formed on the surface of the photosensitive drum. When the static latent image faces the developing unit, toner is supplied from the developing unit to the static latent image to develop the static latent image into a toner image. The toner image is transferred from the photosensitive drum to paper. Thus, image formation onto paper is achieved.
For example, a scorotron charging device has a discharge wire extending in a direction parallel to the rotation axis of a photosensitive drum, a grid electrode interposed between the photosensitive drum and the discharge wire, and shield electrodes formed of metal plates opposed to each other, with the discharge wire therebetween and extending in parallel to the discharge wire. When a high voltage is applied to the discharge wire, corona discharge occurs from the discharge wire. By application of an appropriate voltage to the grid electrode, the amount of electric charge (ions) that reaches the surface of the photosensitive drum is controlled at a constant amount.
In recent years, weight reduction of the process cartridge has been desired.
One method of reducing the weight of the process cartridge is to reduce the thicknesses of the grid electrode and the shield electrodes. However, in some arrangements, the decrease in the thicknesses of the grid electrode and the shield electrodes will decrease the strength of the grid electrode and the shield electrodes along therewith. As a result, the insufficient strength of the grid electrode and the shield electrodes causes problems resulting from deflective deformation in the grid electrode. For example, such problems may include contact between the grid electrode and the photosensitive drum.